For example, there has been known an apparatus for successively making plastic bags each of which comprises a shaped bag including curved opposite side edges, as disclosed in Japanese Patent Publication No. 3,344,958. In the apparatus, a plastic film is fed intermittently in a direction of length thereof. In general, a plurality of plastic films are superposed on each other and fed intermittently. The apparatus includes a Thomson blade which is moved toward and pressed against the plastic films and a receiver when the plastic films are stopped temporarily. The plastic films are therefore sandwiched between and cut by the Thomson blade and the receiver to successively make the plastic bags.
In the apparatus, a plurality of micro connecting portions are formed and spaced from each other along the cut line formed in the plastic films when the plastic films are cut. The micro connecting portions are called micro joints. The plastic films may be cut half in thickness, as disclosed in Japanese Laid-Open Patent Publication No. 2002-224994.
In this case, the plastic films are cut at once when the Thomson blade is pressed against the plastic films and the receiver. The apparatus is therefore problematic in that the Thomson blade has to be pressed with a large force. The force may reach a level of few tons.
In addition, the Thomson blade is mounted on a carriage. The carriage and the Thomson blade are moved by a drive. The apparatus is therefore problematic in that the drive has to have a large capacity to make the Thomson blade pressed with the large force. Furthermore, the Thomson blade has to be pressed against the plastic films and the receiver and uniformly through the cut portion of plastic films, otherwise the plastic films cannot be cut exactly. The Thomson blade may be damaged if being pressed locally and strongly. A parallelism is therefore required between the Thomson blade and the receiver. In this connection, the carriage and the receiver have to be kept from being bent when the Thomson blade is pressed with the large force, to maintain the parallelism between the Thomson blade and the receiver. The carriage and the receiver are therefore required to have rigidity, increasing weight and size. Consequently, the carriage has a large weight to be dangerous when being moved.
It is therefore an object of the invention to provide an apparatus for successively making plastic bags in which a plastic film is cut by a Thomson blade without making the Thomson blade pressed with a large force.